X-ray imaging technique for in vitro tissue composition measurements using saline/iodine displacement: technique optimization

An in vitro radiographic technique which uses saline/iodine displacement has been developed to study the thickness of bone-equivalent and soft-tissue-equivalent materials within atherosclerotic plaques in arterial specimens which have been cut open longitudinally and laid flat. Results concerning the optimization of the imaging parameters are presented and discussed. The technique consists of imaging arterial specimens under two different conditions: (1) when it is immersed in an isotonic saline solution, to estimate the calcium content, and (2) when it is immersed in a concentrated iodine solution, to estimate the total thickness of the specimen. Calibration step wedges made out of bone-mimicking and soft-tissue-mimicking materials are imaged simultaneously to generate calibration curves which are used to convert the radiographs into bone-equivalent and soft-tissue-equivalent thickness images. The optimal spectral parameters were determined to be 45 and 100 kVp for the saline and the iodine images, respectively, with a significant amount of added filtration for both images. Inherent systematic inaccuracies due to (1) the nonidealities due to linear attenuation coefficient mismatch between tissue and calibration materials and (2) beam hardening due to heel effect are determined theoretically, and can be used to correct a set of bone-equivalent and the soft-tissue-equivalent images to within +/- 6 microns with an ideal, noise-free imaging system.